Assessing the Role of Thermal Stresses in Caprock Integrity During CO2 Storage

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Deep saline aquifers provide unbeatable capacities for long term CO2 storage, provided CO2 does not leak. Upon CO2 injection the pressure in the aquifer increases and induces stresses in the caprock. If CO2 is injected at the temperature different from the ambient temperature in the aquifer, there could appear thermal stresses also. We study the effect of CO2 injection temperature on the caprock integrity. Using coupled thermo-poromechanical multi-phase simulations [1], we reveal that thermal expansion of the rock significantly enhances the stresses developing as a result of the fluid pressure buildup. Calculations show that when CO2 is injected at a temperature below the ambient value, the stresses in the caprock above the horizontal injection well become tensile and even exceed the tensile strength after several years of continuous injection [2]. These stresses lead to the caprock fracturing. Once the fractures form, they start to propagate because of the high pressure in the reservoir and may serve as pathways for CO2 leakage. Based on the results of our simulations using the method from [3] we estimate the rate of fracture propagation. We show that this rate is strongly affected by the value of the permeability in the caprock. Finally, our results show that injection of CO2 at temperature close to the ambient value in the aquifer significantly reduces the risk of caprock fracturing and, therefore, possible leakage.